Surface-coated graphite negative electrode material and preparation method thereof

Abstract

The invention provides a graphite negative electrode material, which comprises: graphite having defects; the amorphous carbon is coated on the surface of the graphite; and the lithium niobate is coated on the surface of the amorphous carbon. In the graphite negative electrode material, defects in graphite and the amorphous carbon layer can provide more active sites and a shorter lithium ion diffusion path, so that the rate capability of a battery is improved, and high-rate charging and discharging of the negative electrode of the battery are realized. The lithium niobate coating layer is compact in structure and stable in chemical performance, does not react with sulfide, and can effectively isolate contact between graphite and sulfide electrolyte, so that the stability of the graphite to the sulfide solid electrolyte is improved. Therefore, the graphite negative electrode material disclosed by the invention has relatively high rate capability and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a surface - coated defective graphite negative electrode material and a preparation method thereof. Background Art

[0002] Lithium - ion batteries have the advantages of high energy density, long cycle life, and environmental friendliness, and have a huge market scale in the fields of transportation power, energy storage, 3C digital, and wearable devices. However, commercial liquid lithium - ion batteries have reached the limit of their energy density. With the booming development of the energy industry, higher requirements have been put forward for the rapid storage and efficient utilization of electric energy. Developing next - generation lithium - ion battery technologies with high rate performance, high safety, low cost, and environmental friendliness has become the main goal of the battery industry. All - solid - state lithium batteries use non - flammable solid electrolytes to replace organic electrolytes and separators, fundamentally solving the problem of battery fire caused by thermal runaway. Solid - state lithium - ion batteries, especially sulfide solid - state battery systems with high ionic conductivity, have great application prospects in improving the energy density and rate performance of batteries.

[0003] Developing negative electrode materials suitable for sulfide solid - state battery systems with high ionic conductivity is one of the key challenges for the commercial application of all - solid - state lithium batteries. Among negative electrode materials, graphite negative electrodes have the characteristics of environmental friendliness, low cost, stable process, and low expansion, but still have problems such as interfacial reactions and inability to cycle at high rates in sulfide systems, affecting the rate performance of batteries.

[0004] In summary, the existing graphite negative electrode materials for all - solid - state lithium batteries are difficult to meet the application requirements of batteries in terms of high rate, high stability, and low cost. Therefore, it is urgent to develop new negative electrode materials and their preparation methods. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art to a certain extent. For this purpose, the present invention provides a graphite negative electrode material and a preparation method thereof. The graphite negative electrode material of the present invention has high rate performance and chemical stability.

[0006] Therefore, in the first aspect of the present invention, the present invention proposes a graphite negative electrode material, comprising: graphite, the graphite has defects; amorphous carbon, the amorphous carbon is coated on the surface of the graphite; lithium niobate, the lithium niobate is coated on the surface of the amorphous carbon.

[0007] In the graphite anode material of the present invention, the defects and amorphous carbon layers in the graphite can provide more active sites and shorter lithium-ion diffusion paths, thereby improving the rate performance of the battery and enabling high-rate charge and discharge of the battery anode. The lithium niobate coating layer has a dense structure and stable chemical properties, does not react with sulfides, and can effectively isolate the contact between the graphite and the sulfide electrolyte, thus improving the stability of the graphite towards the sulfide solid electrolyte. Therefore, the graphite anode material of the present invention has high rate performance and stability.

[0008] In some embodiments, based on the total mass of the graphite anode material, the content of graphite ≥ 95%, the content of lithium niobate ≤ 4%, and the content of amorphous carbon ≤ 0.1%.

[0009] In some embodiments, based on the total mass of the graphite anode material, the content of graphite is 95 - 99%, the content of lithium niobate is 1 - 4%, and the content of amorphous carbon is 0.05 - 0.1%; and / or, the particle size of the graphite is 1 - 100 μm.

[0010] In the second aspect of the present invention, a method for preparing the graphite anode material of the first aspect is proposed, including the following steps: introducing defects into the graphite and forming amorphous carbon on the surface to obtain a pre-coated body; formulating the pre-coated body into a dispersion, adding a niobium source solution and a lithium source solution to the dispersion to obtain a mixed solution; and performing heat treatment on the mixed solution to form lithium niobate on the surface of the pre-coated body to obtain the graphite anode material.

[0011] Therefore, the preparation method of the present invention has a low cost and stable process, and the obtained graphite anode material has excellent performance.

[0012] In some embodiments, the method for introducing defects into the graphite and forming amorphous carbon on the surface includes ball milling; during the ball milling process, the parameters are controlled as follows: the ball-to-material ratio is 5:1 - 15:1, the particle size of the ball milling medium is 3 - 10 mm, the ball milling speed is 300 - 500 rpm, and the ball milling time is 0.5 - 2 h.

[0013] In some embodiments, the preparation method satisfies at least one of the following: (1) the solvent of the graphite dispersion includes absolute ethanol, and the mass ratio of the pre-coated body to the solvent is 0.01 - 0.1; (2) the solvent of the niobium source solution includes absolute ethanol, the niobium source includes ethoxyniobium, and the concentration of the niobium source solution is 0.1 - 1 mol / L; (3) the solvent of the lithium source solution includes absolute ethanol, the lithium source includes lithium ethoxide, and the concentration of the lithium source solution is 0.1 - 1 mol / L.

[0014] In some embodiments, the step of performing heat treatment on the mixed solution includes: performing a first heat treatment on the mixed solution to obtain a mixed powder; and then performing a second heat treatment on the mixed powder in an inert atmosphere to form lithium niobate on the surface of the pre-coated body to obtain the graphite anode material.

[0015] In the third aspect of the present invention, a negative electrode plate is proposed, which includes the graphite negative electrode material of the first aspect or the graphite negative electrode material obtained by the preparation method of the second aspect. Thus, the negative electrode plate of the present invention has excellent electrochemical performance.

[0016] In the fourth aspect of the present invention, a lithium-ion battery is proposed, which includes the negative electrode plate of the third aspect; the lithium-ion battery includes a solid-state lithium-ion battery. Thus, the lithium-ion battery of the present invention has high rate performance and chemical stability.

[0017] In some embodiments, the lithium-ion battery further includes an electrolyte, and the electrolyte includes sulfide.

[0018] Compared with the prior art, the beneficial technical effects achieved by the present invention are as follows:

[0019] The present invention proposes that the graphite negative electrode material includes defective graphite, amorphous carbon, and lithium niobate. The amorphous carbon and lithium niobate are coated on the surface of the defective graphite. The defects and amorphous carbon layer of the graphite can provide more active sites and shorter lithium-ion diffusion paths, increase the lithium-ion transmission channels, and accelerate the lithium-ion insertion / extraction process, thereby improving the rate performance of the battery and realizing high-rate charge and discharge of the battery negative electrode. The lithium niobate coating layer has a dense structure and stable chemical properties, does not react with sulfide, and can effectively isolate the contact between graphite and sulfide electrolyte, further improving the stability of graphite to sulfide solid electrolyte. Thus, the graphite negative electrode material of the present invention has high rate performance and stability.

[0020] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0021] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0022] Figure 1 is the transmission electron microscope image of niobate-amorphous carbon-coated graphite in Example 1 of the present invention;

[0023] Figure 2 is the transmission electron microscope image of defective graphite with an amorphous carbon layer generated on the surface after ball milling in Example 1 of the present invention;

[0024] Figure 3 is the intensity ratio diagram of the graphite D characteristic peak and G characteristic peak in the Raman test results of the samples of graphite ball milled for different times in Example 1 of the present invention;

[0025] Figure 4It is a transformation diagram of the orientation degree OI value and the full width at half maximum FWHM value of the (002) characteristic peak in the X-ray diffraction spectrum results of the samples under different ball milling times in Example 1 of the present invention;

[0026] Figure 5 It is a local transmission electron microscope image of lithium niobate-amorphous carbon-coated graphite particles and an energy-dispersive X-ray spectroscopy diagram of carbon, niobium, and oxygen elements on the surface of the graphite layer in Example 2 of the present invention;

[0027] Figure 6 It is an electrochemical impedance spectroscopy diagram of the battery assembled with lithium niobate-amorphous carbon-coated graphite material under different cycle numbers in Example 3 of the present invention;

[0028] Figure 7 It is a cyclic voltammetry curve test diagram of the battery assembled with lithium niobate-amorphous carbon-coated graphite negative electrode material in Example 3 of the present invention;

[0029] Figure 8 It is a voltage-capacity curve of the half-cell assembled with lithium niobate-amorphous carbon-coated graphite negative electrode material at different cycle current densities in Example 3 of the present invention.

[0030] Figure 9 It is a cyclic voltammetry curve test diagram of the half-cell assembled with lithium niobate-amorphous carbon-coated graphite negative electrode material in Example 4 of the present invention;

[0031] Figure 10 It is a cyclic voltammetry curve test diagram of the half-cell assembled with lithium niobate-amorphous carbon-coated graphite negative electrode material in Example 5 of the present invention;

[0032] Figure 11 It is the X-ray diffraction spectrum of the high-crystalline graphite negative electrode material and the obtained orientation degree OI value and the full width at half maximum FWHM value of the (002) characteristic peak in Comparative Example 1 of the present invention;

[0033] Figure 12 It is a cyclic voltammetry curve test diagram of the half-cell assembled with the high-crystalline graphite negative electrode material in Comparative Example 1 of the present invention;

[0034] Figure 13 It is a voltage-capacity curve of the half-cell assembled with the high-crystalline graphite negative electrode material at different cycle current densities in Comparative Example 1 of the present invention;

[0035] Figure 14 It is a cyclic voltammetry curve test diagram of the half-cell assembled with the lithium niobate-coated graphite negative electrode material in Comparative Example 2 of the present invention;

[0036] Figure 15 It is a cyclic voltammetry curve test diagram of the half-cell assembled with the amorphous carbon-coated graphite negative electrode material in Comparative Example 3 of the present invention. Detailed implementation manners

[0037] Embodiments of the present invention will be described in detail below. The embodiments described below are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0038] It should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0039] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0040] In this document, the term "comprising" or "including" is an open expression, that is, it includes the content specified by the present invention, but does not exclude other aspects of the content.

[0041] In the first aspect of the embodiments of the present invention, the present invention provides a graphite anode material, comprising: graphite, the graphite having defects; amorphous carbon, the amorphous carbon coating the surface of the graphite; and lithium niobate, the lithium niobate coating the surface of the amorphous carbon.

[0042] In the graphite anode material provided by the embodiments of the present invention, the defects in the graphite and the amorphous carbon layer can provide more active sites and shorter lithium ion diffusion paths. In particular, the amorphous carbon layer can enhance the adsorption capacity of the graphite surface, increase the lithium ion transport channels, and accelerate the lithium ion insertion / extraction process, thereby improving the rate performance of the battery and realizing high-rate charge and discharge of the battery anode. However, since the amorphous carbon layer will exacerbate the reactivity between the graphite anode and the sulfide electrolyte to a certain extent, it is also necessary to isolate the direct contact between the graphite and the sulfide. The lithium niobate coating layer has a dense structure and stable chemical properties and does not react with sulfides, and can effectively isolate the contact between the graphite and the sulfide electrolyte, thus improving the stability of the graphite to the sulfide solid electrolyte. Thus, the graphite anode material of the present invention has high rate performance and stability.

[0043] In some embodiments of the present invention, based on the total mass of the graphite anode material, the content of graphite is ≥95%, the content of lithium niobate is ≤4%, and the content of amorphous carbon is ≤0.1%.

[0044] The content of graphite ≥ 95% ensures that the main body of the material is still mainly graphite with high theoretical capacity, high electronic conductivity and low cost, avoiding capacity or energy density loss caused by excessive modification. The content of lithium niobate ≤ 4% is beneficial to form a uniform nano-scale ion conductive layer on the surface of graphite, reduce the interfacial impedance, improve the fast charging performance, and at the same time reduce the direct contact between graphite and sulfide electrolyte, improving the stability of graphite to sulfide solid electrolyte. The content of amorphous carbon ≤ 0.1% is beneficial to accelerate the lithium ion transport performance on the surface of graphite. Thus, when the graphite negative electrode material provided by the embodiment of the present invention meets the above conditions, it will have high rate performance and stability.

[0045] In some embodiments of the present invention, based on the total mass of the graphite negative electrode material, the content of graphite is 95-99%, the content of lithium niobate is 1-4%, and the content of amorphous carbon is 0.05-0.1%; and / or, the particle size of graphite is 1-100 μm. Thus, the rate performance and stability of the negative electrode material can be further improved.

[0046] As an example, the content of graphite is 95%, 96%, 97%, 98%, 99%, etc.; the content of lithium niobate is 1%, 2%, 3%, 4%, etc.; the content of amorphous carbon is 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc.

[0047] As an example, the particle size of graphite is 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc.

[0048] In the second aspect of the embodiments of the present invention, the present invention proposes a preparation method of the graphite negative electrode material of the first aspect, including the following steps: introducing defects into graphite and forming amorphous carbon on the surface to obtain a pre-coated body; preparing the obtained pre-coated body into a dispersion liquid, adding a niobium source solution and a lithium source solution to the dispersion liquid to obtain a mixed solution; performing heat treatment on the mixed solution to form lithium niobate on the surface of the pre-coated body to obtain the graphite negative electrode material.

[0049] The preparation method of the graphite negative electrode material provided by the embodiments of the present invention realizes the uniform modification of lithium niobate (LiNbO3) on the surface of graphite through a controllable defect engineering and a liquid-phase coating process. First, defects are introduced into graphite and an amorphous carbon layer is generated on the surface. Then, graphite, a niobium source and a lithium source are dispersed in liquid. Due to the liquid-phase dispersion, the lithium niobate precursor can be uniformly distributed in the internal and external structures of graphite, and a lithium niobate layer is uniformly coated on the internal and external structures of the graphite layer-folded through further heat treatment.

[0050] Those skilled in the art can understand that the features and advantages described above for the graphite negative electrode material also apply to this preparation method, and will not be repeated here.

[0051] In some embodiments of the present invention, the method for introducing defects into graphite and forming amorphous carbon on the surface includes ball milling; in the ball milling process, the control parameters are as follows: the ball-to-material ratio is 5:1 to 15:1, the particle size of the ball milling medium is 3 to 10 mm, the ball milling speed is 300 to 500 rpm, and the ball milling time is 0.5 to 2 h.

[0052] In the embodiments of the present invention, natural spherical graphite is treated by mild ball milling to create defects and simultaneously generate an amorphous carbon structure. The layered structure (sp 2 hybridized carbon layer) of graphite undergoes relative slippage under the shear force of ball milling, resulting in the fracture of the interlayer van der Waals force and the formation of edge defects. At the same time, some carbon atoms transform from planar sp 2 hybridization to tetrahedral sp 3 hybridization, destroying the long-range order and forming amorphous carbon domains. When the ball milling parameters provided in the embodiments of the present invention meet the above conditions, it is beneficial to form defect ports and an amorphous carbon structure on the graphite surface. Thus, the graphite anode material obtained by the preparation method of the present invention will have high rate performance and stability.

[0053] As an example, the ball-to-material ratio is 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, etc.; the particle size of the ball milling medium is 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, etc.; the ball milling speed is 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc.; the ball milling time is 0.5 h, 0.8 h, 1.0 h, 1.2 h, 1.5 h, 1.8 h, 2 h, etc.

[0054] In some embodiments of the present invention, the preparation method satisfies at least one of the following: (1) the solvent of the dispersion liquid includes absolute ethanol, and the mass ratio of the pre-coated body to the solvent is 0.01 to 0.1; (2) the solvent of the niobium source solution includes absolute ethanol, the niobium source includes niobium ethoxide, and the concentration of the niobium source solution is 0.1 to 1 mol / L; (3) the solvent of the lithium source solution includes absolute ethanol, the lithium source includes lithium ethoxide, and the concentration of the lithium source solution is 0.1 to 1 mol / L.

[0055] In the preparation method provided by the embodiments of the present invention, since the surface of graphite is hydrophobic and it is easy to agglomerate in an aqueous solution, ethanol has a moderate polarity, can wet the surface of graphite but will not cause violent oxidation. Ethoxy niobium and lithium ethoxide have good solubility in absolute ethanol and can form a transparent solution with molecular-level dispersion, avoiding particle agglomeration. The addition amounts of the niobium source solution and the lithium source solution are determined according to the lithium niobate coating amount. In addition, due to the moderate volatility of ethanol, it is convenient to quickly evaporate during the subsequent heat treatment process, which is beneficial to forming a uniform lithium niobate coating layer on the surface of graphite. When the solution concentration provided by the embodiments of the present invention meets the above conditions, it is beneficial to form defect ports and amorphous carbon structures on the surface of graphite. Therefore, the preparation method of the present invention can obtain a graphite negative electrode material with excellent performance.

[0056] As an example, the mass ratio of graphite to absolute ethanol is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc.; the concentration of the niobium source solution is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc.; the concentration of the lithium source solution is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc.

[0057] In some embodiments of the present invention, the step of heat-treating the mixed solution includes: performing a first heat treatment on the mixed solution to obtain mixed powder; and then performing a second heat treatment on the mixed powder in an inert atmosphere to form lithium niobate on the surface of the pre-coated body, thereby obtaining a graphite negative electrode material.

[0058] In the first heat treatment of the embodiment of this method, the mixed solution is kept stirred under heating conditions to completely volatilize ethanol and obtain mixed powder. Then, the mixed powder is subjected to a second heat treatment (such as calcination) in an argon atmosphere. After cooling, the powder body can be a lithium niobate-coated defective graphite negative electrode. Therefore, the preparation method of the present invention can obtain a graphite negative electrode material with excellent performance.

[0059] In some embodiments of the present invention, the temperature of the first heat treatment is 80 - 110 °C; and / or, the temperature of the second heat treatment is 300 - 400 °C, the time is 1 - 2 h, and the heating rate is 2 - 10 °C / min.

[0060] As an example, the temperature of the first heat treatment is 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, etc.; the temperature of the second heat treatment is 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, etc.; the time is 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, etc.; the heating rate is 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, etc.

[0061] In the third aspect of the present invention, the present invention provides a negative electrode sheet, which includes the graphite negative electrode material of the first aspect or the graphite negative electrode material obtained by the preparation method of the second aspect. Thus, the negative electrode sheet of the present invention has excellent electrochemical performance.

[0062] In the fourth aspect of the present invention, the present invention provides a lithium-ion battery, which includes the negative electrode sheet of the third aspect; the lithium-ion battery includes a solid-state lithium-ion battery. Thus, the lithium-ion battery of the present invention has excellent electrochemical performance.

[0063] In some embodiments of the present invention, the lithium-ion battery further includes an electrolyte, and the electrolyte includes a sulfide.

[0064] The solution of the present invention will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those without specific technical or conditions noted in the embodiments, the techniques or conditions described in the literature in the art or according to the product specifications are followed. Those reagents or instruments without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0065] Example 1: Formation of defects and amorphous carbon layers in graphite

[0066] Put the high-crystalline graphite raw material with a particle size of 30 μm into a ball milling device for ball milling. The ball milling parameters are set as follows: the ball-to-material ratio is 10:1, the particle size of the ball milling medium is 5 mm, the ball milling speed is 400 rpm, the ball milling time is 1 h, and the content of amorphous carbon is 0.1%. At the same time, at a fixed ball-to-material ratio, medium particle size, and ball milling speed, the ball milling time is changed to 2 h, 4 h, 8 h, and 12 h respectively to prepare ball milled samples with different degrees for comparison. The ball milled samples are shown by Figure 1 and Figure 2 There are multiple defect ports on the surface of the graphite layer. The defect is the lithium ion inlet and outlet channel, and there is an amorphous carbon layer outside the notch.

[0067] In order to further analyze the characteristics of graphite with different ball milling degrees, Raman tests and X-ray diffraction tests are carried out on samples with different ball milling times at a fixed ball-to-material ratio, medium particle size, and ball milling speed. FromFigure 3 From the Raman results, it can be seen that as the ball milling time increases, the sp 3 hybrid characteristic peak D peak intensity I D and the sp 2 hybrid characteristic peak G peak I G ratio gradually increases, and the degree of defect of graphite continuously increases. From Figure 4 the X-ray diffraction test pattern, it can be seen that as the ball milling time increases, the orientation degree OI of graphite continuously decreases, indicating that increasing the ball milling time can increase the degree of defect of graphite, increase the lithium ion insertion sites, and improve the rate performance of graphite. However, at the same time, too long ball milling time will cause the full width at half maximum FWHM of the (002) characteristic peak to continuously increase, and the amorphous degree of graphite continuously increases. Excessive amorphous degree will increase the reactivity with sulfide electrolyte and affect the cycle stability of the negative electrode. According to I D / I G , OI and FWHM 002 The change trend shows that when ball milling for 0.5 - 2 h, the increase degree of the amorphous degree FWHM 002 is relatively weak, and at the same time, the OI value and I D / I G change significantly, meeting the characteristics required for mild ball milling, that is, increasing the defect ports but with a weak amorphous degree, which provides more channels for lithium ions to insert into graphite and effectively improves the rate performance of graphite.

[0068] Example 2: Preparation of lithium niobate coating layer on the surface of graphite

[0069] Disperse the spherical graphite with a ball milling time of 1 h in Example 1 in an absolute ethanol solution. The mass ratio of graphite to absolute ethanol is 0.5, and the dispersion time is 2 h. Then prepare ethoxy niobium solution and lithium ethoxide solution with a concentration of 1 mol / L each.

[0070] Dropwise add the ethoxy niobium solution and lithium ethoxide solution into the spherical graphite dispersion liquid respectively, and keep stirring and dispersing. In this example, coat 15 g of graphite ethanol dispersion liquid. Finally, the mass ratio of graphite in the coated sample is 99%, and the mass ratio of lithium niobate is 1%. The required ethoxy niobium solution and lithium ethoxide solution are both 0.34 mL.

[0071] Keep stirring the mixed solution under heating conditions until the ethanol volatilizes completely; the heating temperature is 80 °C, and the stirring speed is 600 rpm to obtain a dry mixed powder.

[0072] Calcine the dry mixed powder in an argon atmosphere. After cooling, the powder can be the lithium niobate-coated graphite negative electrode; the calcination time is 1.5 hours, the calcination temperature is 350 °C, and the heating rate is 5 °C / min.

[0073] AsFigure 5 As shown, a single-particle graphite was cut by a focused ion beam, and energy-dispersive X-ray spectroscopy analysis was performed on the surface of the internal structure of the graphite. From the transmission electron microscope, the inner-layer folded structure of the graphite could be observed. The green area representing carbon elements was evenly and densely distributed, and an orange pixel aggregation representing niobium elements and a red pixel aggregation representing oxygen elements were evenly distributed on the outer layer of the graphite.

[0074] The results show that the lithium niobate coating method can uniformly coat the coating material on the surfaces of each layer of graphite inside and outside the graphite. At the same time, the thickness of the coating layer can be adjusted by controlling the coating amount. In this embodiment, the obtained coating layer thickness is about 15 nm.

[0075] Example 3: Investigation of the performance of the lithium niobate-coated graphite anode material

[0076] The lithium niobate-coated graphite prepared in Example 2 was fully mixed with a lithium phosphorus sulfur chlorine electrolyte (Li6PS5Cl) at a mass ratio of 7:3 as a mixed anode material, and a half-cell was formed with the lithium phosphorus sulfur chlorine electrolyte and a lithium indium alloy as the counter electrode. The impedance diagram changes at different cycle numbers were tested, and the results are as Figure 6 shown. As can be seen from Figure 6 , after the first cycle, the impedance increased by about 3 Ω, and there was no obvious increase in impedance in subsequent cycles. This indicates that the lithium niobate-coated graphite anode material of the present invention has good stability.

[0077] Furthermore, cyclic voltammetry testing was performed on this half-cell, and the results are as Figure 7 shown. At a scanning rate of 0.1 mV / s and an active material loading of 7.64 mg / cm 2 , the highest oxidation peak current density reached by the lithium niobate-coated graphite anode material was 3.16 mA / cm 2 . This peak current reflects to a certain extent the lithium deintercalation / insertion ability of the system. The electrochemical reaction current in the irreversible reaction region (>0 V) was small, indicating that the system has high stability. The battery was cycled at current densities of 0.05 mA / cm 2 , 0.1 mA / cm 2 , 0.2 mA / cm 2 , 0.5 mA / cm 2 , 1 mA / cm 2 and 2 mA / cm 2 , and the results are as Figure 8 shown. The lithium niobate-coated graphite anode material can release a specific capacity of 282 mAh / g at a current density of 0.05 mA / cm 2 , and the specific capacity can be maintained at 100 mAh / g at a current density of 2 mA / cm 2 .

[0078] The results show that the graphite negative electrode material of the present invention can effectively improve the rate performance and energy density of the battery.

[0079] Example 4:

[0080] The difference between Example 4 and Example 1 is that the content of amorphous carbon in Example 4 is 0.05%. The remaining preparation steps are the same as those in Example 2 and Example 3.

[0081] Furthermore, cyclic voltammetry tests were performed on this half-cell, and the results are as Figure 9 shown. At the same scanning rate and active material loading, the highest oxidation peak current density reaches 3.12 mA / cm 2 , and this peak current reflects to a certain extent that the system has high rate performance. The electrochemical reaction current in the irreversible reaction region is small, indicating that the system has high stability.

[0082] The results show that the graphite negative electrode material of the present invention can effectively improve the rate performance and energy density of the battery.

[0083] Example 5:

[0084] The difference between Example 5 and Example 2 is that in Example 5, 15 g of graphite ethanol dispersion is coated, and finally the mass ratio of graphite in the obtained coated sample is 95.9%, and the mass ratio of lithium niobate is 4%. The required niobium ethoxide solution and lithium ethoxide solution are both 1.41 mL. The remaining preparation steps are the same as those in Example 1 and Example 3.

[0085] Furthermore, cyclic voltammetry tests were performed on this half-cell, and the results are as Figure 10 shown. At the same scanning rate and active material loading, the highest oxidation peak current density reaches 2.89 mA / cm 2 , and this peak current reflects to a certain extent that the system has high rate performance. The electrochemical reaction current in the irreversible reaction region is small, indicating that the system has high stability.

[0086] The results show that the graphite negative electrode material of the present invention can effectively improve the rate performance and energy density of the battery.

[0087] Comparative Example 1:

[0088] The graphite in Comparative Example 1 is highly crystalline graphite, without the formation of defects and amorphous carbon layers, and there is no lithium niobate coating layer on the graphite surface. The X-ray diffraction pattern and the obtained orientation degree OI value and the full width at half maximum FWHM value of the (002) characteristic peak are as Figure 11 shown, and the method for investigating the performance of the graphite negative electrode material is the same as that in Example 3.

[0089] Furthermore, cyclic voltammetry tests were performed on this half-cell, and the results are as Figure 12As shown. At the same scanning rate and active material loading, the highest oxidation peak current density reaches 1.46 mA / cm 2 , the electrochemical reaction current in the irreversible reaction region is small, indicating that this system has good stability but general rate performance. The battery was cycled at current densities of 0.05 mA / cm 2 , 0.1 mA / cm 2 , 0.2 mA / cm 2 , 0.5 mA / cm 2 , 1 mA / cm 2 and 2 mA / cm 2 . The results are as shown in Figure 13 . The lithium niobate-coated graphite anode material can release a specific capacity of 212 mAh / g at a current density of 0.05 mA / cm 2 . At a current density of 2 mA / cm 2 , the specific capacity can only be maintained at 15 mAh / g.

[0090] Comparative Example 2:

[0091] There is no formation of defects and amorphous carbon layers in the graphite of Comparative Example 2, but there is a lithium niobate coating layer on the graphite surface. The lithium niobate coating layer on the graphite surface was prepared according to the steps of Example 2. The method for investigating the performance of the graphite anode material is the same as that of Example 3.

[0092] Furthermore, cyclic voltammetry tests were performed on this half-cell, and the results are as shown in Figure 14 . At the same scanning rate and active material loading, the highest oxidation peak current density reaches 1.54 mA / cm 2 , and the electrochemical reaction current in the irreversible reaction region is small, indicating that this system has good stability but general rate performance.

[0093] Comparative Example 3:

[0094] There is no lithium niobate coating layer on the graphite surface of Comparative Example 3, but there are defects and amorphous carbon layers in the graphite. The defects and amorphous carbon layers in the graphite were prepared according to the steps of Example 1. The method for investigating the performance of the graphite anode material is the same as that of Example 3.

[0095] Furthermore, cyclic voltammetry tests were performed on this half-cell, and the results are as shown in Figure 15 . At the same scanning rate and active material loading, the highest oxidation peak current density reaches 2.06 mA / cm 2 , and the electrochemical reaction current in the irreversible reaction region is large, indicating that this system improves the rate performance to a certain extent, but has poor stability, and the side reaction products further affect the rate performance and cycle stability of the system.

[0096] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0097] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A graphite anode material, characterized in that, Comprising: Graphite, wherein the graphite has defects; Amorphous carbon, wherein the amorphous carbon coats the surface of the graphite; Lithium niobate, wherein the lithium niobate coats the surface of the amorphous carbon.

2. The graphite negative electrode material according to claim 1, characterized in that, Based on the total mass of the graphite negative electrode material, the content of the graphite is ≥95%, the content of the lithium niobate is ≤4%, and the content of the amorphous carbon is ≤0.1%.

3. The graphite anode material according to claim 1 or 2, characterized in that Based on the total mass of the graphite negative electrode material, the content of the graphite is 95 - 99%, the content of the lithium niobate is 1 - 4%, and the content of the amorphous carbon is 0.05 - 0.1%; And / or, the particle size of the graphite is 1 - 100 μm.

4. A method for preparing the graphite anode material according to any one of claims 1 to 3, characterized in that, Including the following steps: Introducing defects into the graphite and forming amorphous carbon on the surface to obtain a pre-coated body; Formulating the pre-coated body into a dispersion liquid, adding a niobium source solution and a lithium source solution to the dispersion liquid to obtain a mixed solution; Performing heat treatment on the mixed solution to form lithium niobate on the surface of the pre-coated body to obtain a graphite negative electrode material.

5. The method according to claim 4, characterized in that, The method for introducing defects into the graphite and forming amorphous carbon on the surface includes ball milling treatment; in the ball milling treatment, the control parameters are: the ball-to-material ratio is 5:1 - 15:1, the particle size of the ball milling medium is 3 - 10 mm, the ball milling speed is 300 - 500 rpm, and the ball milling time is 0.5 - 2 h.

6. The method according to claim 4 or 5, characterized in that Satisfying at least one of the following: (1) The solvent of the dispersion liquid includes absolute ethanol, and the mass ratio of the pre-coated body to the solvent is 0.01 - 0.1; (2) The solvent of the niobium source solution includes absolute ethanol, the niobium source includes niobium ethoxide, and the concentration of the niobium source solution is 0.1 - 1 mol / L; (3) The solvent of the lithium source solution includes absolute ethanol, the lithium source includes lithium ethoxide, and the concentration of the lithium source solution is 0.1 - 1 mol / L.

7. The preparation method according to claim 4, characterized in that, The step of performing heat treatment on the mixed solution includes: Performing a first heat treatment on the mixed solution to obtain a mixed powder; Then performing a second heat treatment on the mixed powder in an inert atmosphere to form lithium niobate on the surface of the pre-coated body to obtain a graphite negative electrode material.

8. A negative electrode sheet, characterized in that, Including the graphite negative electrode material according to any one of claims 1 to 3 or the graphite negative electrode material obtained by the preparation method according to any one of claims 4 to 7.

9. A lithium-ion battery, characterized in that, Including the negative electrode plate according to claim 8; the lithium ion battery includes a solid state lithium ion battery.

10. The lithium ion battery according to claim 9, wherein, It further includes an electrolyte, and the electrolyte includes sulfide.

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